The following abbreviations are utilized herein:    802.11s mesh networking described by the IEEE 802.11s draft amendment    ACK acknowledgement (acknowledgement message)    AP access point    ATIM announcement traffic indication message    DTIM delivery traffic indication message    DS distribution system    GAS generic advertisement service    IBSS independent basic service set    EEEE institute of electrical and electronics engineers    MAC medium access control (layer 2, L2)    MAP mesh access point    MIMO multiple input/multiple output    MP mesh point    MSDU MAC service data unit    STA station    TBTT target beacon transmission time    TIM traffic indication message    WiMAX worldwide interoperability for microwave access (IEEE 802.16 standard)    WLAN wireless local area network
One publication of interest to the ensuing description is: IEEE P802.11s™/D1.07, Draft STANDARD for Information Technology-Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: ESS Mesh Networking (September 2007).
In accordance with draft 1.07 of 802.11s, coordination of devices within radio range is achieved by the exchange of beacon frames. Periodic beacon transmission enables device discovery, supports dynamic network organization, and provides support for mobility.
As described in the IEEE P802.11s™ Draft Standard, in section 5.2.9.1 “Introduction to mesh”, in WLAN deployments without mesh services, stations (STAs) must associate with an AP in order to gain access to the network. These STAs are dependent on the AP with which they are associated to communicate. An example of a non-mesh WLAN deployment model and device classes are illustrated herein in FIG. 1, which reproduces FIG. s1 of the IEEE P802.11s™ Draft Standard.
Many WLAN devices can benefit from support for more flexible wireless connectivity. Functionally, the Distribution System (e.g., the traditional backbone which over which the APs are connected) of an AP can be replaced with wireless links or multi-hop paths between multiple APs. Devices traditionally categorized as clients can benefit from the ability to establish peer-to-peer wireless links with neighboring clients and APs in a mesh network.
An example mesh is illustrated in FIG. 2, which reproduces FIG. s2 of the IEEE P802.11s™ Draft Standard. Mesh points (MPs) are entities that support mesh services, i.e., they participate in the formation and operation of the mesh network. An MP may be co-located with one or more other entities (e.g., AP, portal, etc.). The configuration of an MP that is co-located with an Access Point is referred to as a MAP. Such a configuration allows a single entity to logically provide both mesh functionalities and AP functionalities simultaneously. STAs associate with APs to gain access to the network. Only MPs participate in mesh functionalities such as path selection and forwarding, etc. Mesh portals (MPPs) interface the network to other IEEE 802 LAN segments.
As is stated in section 5.2.9.2, “Mesh network model”, of the IEEE P802.11s™ Draft Standard, a mesh network is an IEEE 802 LAN comprised of IEEE 802.11 links and control elements to forward frames among the network members. Effectively, this means that a mesh network appears functionally equivalent to a broadcast Ethernet from the perspective of other networks and higher layer protocols. Thus, it normally appears as if all MPs in a mesh are directly connected to the link layer. This functionality is transparent to higher layer protocols. Reference in this regard can be made to FIG. 3A, which reproduces FIG. s-3 of the IEEE P802.11s™ Draft Standard. It should be noted that while this figure shows the forwarding of data over multiple hops, there may also be direct data transfer over a single hop, such as is shown in FIG. 3B, wherein the source and destination of the MSDUs are within a one-hop neighborhood, and where no forwarding, routing or link metric need be used.
An Awake Window is the time period after TBTT during which frame delivery initiation messages may be transmitted. An ATIM frame is used after beacon frame to initiate frame transmissions. An IBSS mode has beacons, similarly as infrastructure mode. IBSS beacon transmission and infrastructure beacon transmission rules differ. In infrastructure beaconing one AP transmits one beacon, in IBSS multiple stations compete for a beacon transmission opportunity, and a given station either receives a beacon from another station in the same IBSS network or transmits a beacon. Specifically, in the awake window only the beaconing mesh point operates in the active mode, whereas in the IBSS ATIM window all of the mesh points operate in the active mode. Reference in this regard may be had to IEEE 802.11-1999 reaff 2003, sections 11.1.2.1 and 11.1.2.2. 802.11s specifies that the Awake Window which is similar to the ATIM period is used after the infrastructure or IBSS beacon, if the MP operates in power save mode.
The packet sets the synchronization of the group and announces that messages are waiting to be delivered. Stations in power save mode wake up periodically to listen for ATIM packets in ad hoc (IBSS) networks, just as they do for Beacon packets in infrastructure (BSS or ESS) networks.
A power-consumption problem exists in the foregoing and other types of wireless networks that is related to a need to minimize the activity time of a MP, such as the periodic media listening time of the MP. The receiving of the beacons of other MPs can consume a significant amount of power, especially if the beacons are transmitted separately, each at its own appointed time. The power consumption problem is particularly of concern in battery powered MPs.
As currently specified the MP is expected to receive all peer MPs beacons, i.e., all MPs to which the local MP has a link, and remain active during its own beacon plus the ATIM period time.
Three representative publications that generally address power management in IEEE 802.11 networks include:    “Optimal ATIM size for 802.11 networks in ad hoc mode”, X. Gao et al., DoCoMo Communications Lab USA (2006);    US Patent Publication No.: 2007/0133448, Jun. 14, 2007, “Method and Apparatus for Optimal ATIM Size Setup for 802.11 Networks in an Ad Hoc Mode”, X. Gao et al.; and    US Patent Publication No.: 2006/0251004, Nov. 9, 2006, “Power Management in an IEEE 802.11 IBSS WLAN Using an Adaptive ATIM Window”, Z. Zhong et al.
In accordance with section 11A.11 of draft 1.07 of the 802.11s amendment, a MP indicates its power management by setting a “Current Power Management Mode” bit in the power save capability field of the Mesh Capability element in its beacons and by sending a frame with the Power Management bit in the frame control field set (e.g., the frame control field of a MAC frame).